Chemical Composition of the Marc of a Wild Tropical Plant Tacca involucrata (Schumach and Thonn, 1827)

摘要

Tacca involucrata (Batflower or Polynesian arrowroot) tubers are a stable food in tropics where it occurs. In central Nigeria, it is processed locally after digging it from the ground by peeling with sharp sand, grating and soaking in fresh water after which it is filtered and the filtrate is dried and is cooked with other ingredients. The marc, said to be bitter, is usually discarded by deep burial as it is considered poisonous to livestock and humans. All parts of the plant are used in folk medicine to treat various diseases. The aim of this work was to analyze quantitatively the phytochemical, elemental, vitamin and proximate composition of the marc of the tubers with a view of assessing its pharmacological and nutritional potentials. The marc was obtained from Jandeikyura Village in Wukari LGA of Taraba State, Nigeria, and was extracted with 80% methanol for 72 hr to give a yield of 10.1% w/w and was whitish in colour. Phytochemical analysis showed the presence of reducing sugars, tannins, flavonoids, steroids, glycosides and hydrogen cyanide at 195.65 ± 0.5, 3.44 ± 0.2, 1.29 ± 0.5, 0.83 ± 0.4, 1.36 ± 1.0 and 0.00985 ± 0.3 (mg/100g), respectively. The elemental analysis showed the presence of potassium, sodium, magnesium, selenium, manganese, vanadium and some heavy metals like lead, aluminium, arsenic and mercury at 36.45 ± 0.1, 44.04 ± 0.1, 1.52 ± 0.2, 0.80 ± 0.9, 0.52 ± 0.7, 0.27 ± 0.7, 0.07 ± 0.6, 0.008 ± 0.05, 0.085 ± 0.6 and 0.026 ± 0.6 (mg/100g), respectively. Vitamin analysis showed the presence of vitamins A, B1, B2, B3, C and E in various amount as 2.26 ± 0.8 μg, 0.83 ± 0.8 mg/100g, 0.58 ± 0.4 mg/100g, 0.33 ± 0.6 mg/100g, 9.80 ± 0.4 mg/100g and 6.86 ± 0.9 mg/100g, respectively. The proximate analysis showed the marc to contain moisture, ash, fats, fibre, crude protein and carbohydrate in the range of 10.83% ± 0.3%, 1.93% ± 0.6%, 1.06% ± 0.5%, 4.42% ± 0.4%, 6.12% ± 0.6% and 86.07% ± 0.3%, respectively. This shows that despite the presence of hydrogen cyanide and some heavy metals in traces amount which are considered poisonous to livestock and humans, the marc contains some elements, vitamins, phytochemical and nutrients which are pharmacologically and nutritionally important.